Secondary-electron-emitting discharge device



Dec; 25, 1951 c. s. BULL 2,579,786

SECONDARY-ELECTRON-EMITTING DISCHARGE DEVICE Filed April 15. 1948 CabdSeafcm Bull By AHOTTley Patented Dec. 25 1951 SECONDARY-IDLE CTRON-"EMITTIN G DISCHARGE DEVICE Cabot Seaton Bull, Hillingdon, England,assignor to Electric & Musical Industries Limited, Hayes,

Middlesex, Britain England, a company of Great Application April 15,1948, Serial No. 21,136 In Great Britain April 18, 1947 9 Claims.

This invention relates to discharge devices employingsecondary-olectron-emission.

Various proposals have been made heretofore for the construction ofso-called multi-stage electron discharge devices employingsecondary-electron-emission, comprising a thermionic cathode foremitting a beam of primary electrons, a control electrode whereby thethermionic emission from said cathode can be controlled, a secondaryelectron-emitting electrode (hereinafter and in the claims referred tofor convenience as a dynode) on which said beam of electrons can becaused to impinge so as to release secondary electrons, at least onefurther dynode on which said secondary electrons can be caused toimpinge so as to release further secondary electrons, and a collectingelectrode for collecting secondary electrons released from said latterdynode. Electron discharge devices of this kind are referred tohereinafter and in the claims as devices of the kind described.

Such devices would be particularly suitable for use as amplifyingvalves, the signals to be amplified being applied to said controlelectrode and an amplified output of said signals being obtained at saidcollecting electrode. However the devices which have been proposedhitherto have given rise to constructional and electron-opticaldifficulties and the object of the present invention is to provide animproved electron discharge device of the kind described with a view toreducing these difficulties.

According to the present invention an electron discharge device of thekind described is provided, wherein said first dynode comprises asecondary-electron-emitting surface which is located beyond said seconddynode when viewed from said thermionic cathode, and wherein theelectrodes in said device are so arranged that when appropriatepotentials are applied thereto a beam of primary electrons is projectedfrom said thermionic cathode at an acute angle to a plane containingsaid cathode and said second dynode whereby said beam is caused to passsubstantially wholly to one side of said second dynode and impinge onsaid first dynode.

In order that the said invention may be clearly understood and readilycarried into effect, the same will now be more fully described withreference to the accompanying drawings, in which- Figure 1 is atransverse sectional view of an electron discharge device according toone embodiment of the present invention,

Figures 2 and 3 illustrate modifications of said embodiment, and

Figure 4- is a transverse sectional view according to anotherembodimentof the present invention.

Referring first to Figure 1 of the drawings, reference numeral Iindicates a thermionic: cathode which is of elongated formhaving arectangular transverse section as shown in the drawings, the wider sidesof the cathode being e1ectron-emissive'. control electrode 2 which is awire -wound electrode supported by support: rods 3 and surrounding thecontrol electrodeis an accelerating electrode 4 which is also a wir'e'wound electrode supported by support rods 5. Surrounding the electrodestructure so far described is a dynode 6 which is preferably in the formof a continuous sheet of metal shaped so that it is elliptical intransverse section as shown, the major axis and the minor axis of theellipse being indicated by the chain dotted lines 20 and 21 respectivelyso that the longitudinalaxis of the dynode is represented by theintersection 22 of the axes 20 and 21, said last mentionedaxis being ofcourse normal to the plane of the drawing. The inner surface of saiddynode 6 is provided with a coat ing of secondary-electron emittingmaterial indicated by the dotted lines 6d. The coating may be such as isdescribed in British Patent No. 601,966 and is providedonareas adjacentto the ends of the major axis 20 on opposite sides thereof. Disposedwithin the elliptical dynode 6 and near the ends of themajor axis 2|] isa pair of further dynodes land 8, these dynodes and 8 being located oneither side of thecathode I, as

shown and being preferably in the form of tubes having a'circular'cross-section and also coated on their surfaces,where'electrons emitted by the electrode 6 impinge, withsecondary=electronemitting material. and 8: are anodes 9 and [0 whichare preferably helices wound from wire and-supported by support rods IIand I ZL-an'd between the dynodesl and 8 and thecathode I there aredisposed focussing electrodes l3 an'd M which are'i'n the form ofrod-shaped electrodes The electrode structure is, as stated, shown intransverse section in Figure 1 audit will be appreciated that the lengthof the various electrodes in a'plane normal to that of the drawing maybe of any desired length. The dynodes T- and 8-and the focussingelectrodes I3 and M are disposed with their longitudinal axesin theplane containingthe longitudinal axis 22 and also the major axisSurrounding the cathode l is a Surrounding the dynodes l plane alsocontains the common longitudinal axis of the cathode I, controlelectrode 2 and accelerating electrode 4. Moreover these latterelectrodes, in transverse section as shown, have a common major axis 23and a common minor axis 24,and saidmajor axis is disposed at an anglewith respect to the major axis of the elliptical dynode 6 of not lessthan and not greater than 70, the preferred inclination being this beingthe inclination shown in the drawings. The electrode structure isarranged in usual manner in a suitable evacuated glass envelope I5.

In operation of the discharge device shown, the cathode may bemaintained at earth potential, the control electrode 2 at a suitablenegative potential so that signals applied to the control electrodecause a variation in the thermionic emission from cathode I. Theaccelerating electrode 4 may be maintained atia positive potential ofabout 150 volts, the dynode 6 at a positive potential of about 250volts, the dynodes l and 8 at positive potentials of about 400 volts andthe anodes 9 and II] at positive potentials of about 600 volts. Theelectrodes l3 and I4 may be maintained at the potential of the cathode Ior at the potential of the electrode 4. On applying these potentials tothe electrodes, primary electrons are emitted from the wider sides ofthe cathode I in the form of oppositely directed beams, which are fairlywell defined as indicated by the dotted lines, each beam being projectedat an acute angle (about 50 in this example), to the plane containingthe longitudinal axes of the cathode I, and the dynodes I and 8. Afterleaving the cathode I the beams are deflected by the combined field dueto the anodes 9 and I9 and the dynodes 1 and 8, but the angle at whichthey leave the cathode I is nevertheless such that they are caused topass substantially wholly to one side of the respective dynodes I and 8and impinge on the surface of the dynode 6 near the anodes 9 and II] asshown, the electron-emitting surfaces of the dynodes 6 as seen from thecathode I being of course located beyond the dynodes I and 3. The sidesof the beams nearer the anodes 9 and I0 are prevented from beingdeflected and so impinging on said anodes and the dynodes I and 8 bymeans of the electrodes I3 and I4. The primary beams of electronsrelease secondary electrons from the dynode 6 and these secondaryelectrons are then caused to impinge on the further dynodes I and 8 fromwhich further secondary electrons are emitted which are collected by theanodes 9 and I9.

It is preferred to make the shape of the dynode 6 elliptical, as shown,since the areas thereof from which secondary electrons are emitted arethereby brought closer to the anodes 9 and II]. The shape of the anodes9 and II) in transverse section where they face the areas from whichsecondary electrons are emitted from the dynode 6 are preferablycircular, as shown, so that the secondary electrons emitted by thedynode 6 pass substantially normally through the anodes 9 and II) on tothe dynodes I and 8. The capacity between the anodes 9 and I0 and thecontrol electrode 2 is substantially eliminated by the provision ofchannel-shaped shields I6 disposed adjacent the accelerating electrode4, and attached to the focussing electrodes I3 and I4, as described inthe specification of the aforesaid co-pending application. The shieldsIt may however, if desired, be attached to the accelerating electrode 4,instead of the focussing electrodes.

The cathode I preferably has the rectangular transverse section shown,but may, if desired, be of elliptical form in transverse section asillustrated in Figure 2 in which case the electrodes 2 and 4 may also beelliptically-shaped in transverse section as illustrated. It may, insome cases, be possible to employ a cathode of circular form intransverse section as illustrated in Figure 3. In this case in order toconcentrate the electrons emitted from the cathode I so as to form twooppositely directed beams at an acute angle to the plane containing thelongitudinal axes of the cathode I and the dynodes T and 8, the controlelectrode 2 and the accelerating electrode 4 have, in transversesection, a major axis and a minor axis with the supporting rods 3 and 5disposed on the major axis and with the major axis inclined at an acuteangle to said plane, while two channel-shaped beam-forming electrodes I!and I8 are provided adjacent opposite ends of said major axis. Bysuitably varying the inclination of the electrodes 2, 4, II and I8 itshould be possible to avoid the risk of the beams from the circularcathode impinging on the anodes 9 and I9.

Anelectron discharge device with the electrode structure shown in Figure1 has the disadvantage that the leads required to connect the dynodes Iand 8 together, and the anodes 9 and II! together, will be ofconsiderable length. In order to reduce the length of leads required theelectrode structure shown in Figure 4 may beemployed. In this figureelectrodes which correspond to those shown in Figure 1 are given thesame reference numerals. The electrode structure shown in Figure 4 is adevelopment of that shown in Figure 1 and is obtained by replacingone-half of the electrode structure shown in Figure 1 by the mirrorimage of the remaining half taken along the plane containing thelongitudinal axis and also the major axis 23 of the electrodes I, 2 and4, said plane being of course substantially normal to the directions inwhich the oppositely directed beams leave the cathode I. The dynode 6therefore comprises a structure each half of which conforms in crosssection to part of an elliptical surface whose major axis is inclined tothe major axis of the other half, the major axis of the halves beingindicated respectively by the chain dotted lines 25 and 26. It will beobserved from Figure 4 that the anodes 9 and ID are thus disposed closertogether and near to one edge of the screening electrode 4. Hence, thelength of the leads required to connect the dynodes 7 and 8 together andthe anodes 9 and Iii together can be made shorter, thus reducing theinductance of the leads and resulting in a simplification in thestructure of the device in so far as concerns the screening of the anodeleads and the lead to the control electrode 2 from one another. InFigure 2, only a single channel section screen I5 is employed, insteadof two as in Figure 1, attached to the focussing electrodes I3 and I4,as shown or, if desired to the screening electrode 4.

I claim:

1. In a multi-stage electron discharge device which utilises secondaryelectron emission for obtaining amplification, a thermionic cathode, acontrol electrode for controlling thermionic emission from said cathode,a first dynode comprising a structure conforming to a closed curvedsurface, a second dynode, said thermionic cathode and said second dynodebeing enclosed by said surface, an electrode for collecting secondaryelectrons from said second dynode, and means for projecting theelectrons released from said cathode in a beam at an angle to passsubstantially wholly to one side of said second dynode and impinge onthe inner side of said first dynode, whereby to release secondaryelectrons which can impinge on said second dynode.

2. In a multi-stage electron discharge device which utilises secondaryelectron emission for obtaining amplification, a thermionic cathode, a

control electrode for controlling thermionic emission from said cathode,a first dynode comprising a structure conforming to at least part of asurface of substantially elliptical cross section, said structureprovided with secondary electron emissive material on an area on theinner side adjacent one end of the major axis of said surface, a seconddynode enclosed by said surface and intersected by the plane containingsaid major axis and the longitudinal axis of said surface, said cathodebeing also enclosed by said surface and intersected by said plane on theother side of said second dynode from said end of the major axis, anelectrode for collecting secondary electrons from said second dynode,and means for projecting electrons released from said cathode in a beamat an acute angle to said plane to pass substantially wholly to one sideof said second dynode and impinge on said area, whereby to releasesecondary electrons which can impinge on said second dynode.

3. In a device according to claim 2, said cathode comprising a tubularmember having in cross section a major axis and a minor axis, thelongitudinal axis of said cathode member being disposed in said planewhile the major axis of said cathode member is disposed at an angle tosaid plane of to 70 degrees.

4. In a device according to claim 2, said beam projecting meanscomprising an electrode structure having in cross section a major axisand a minor axis, the longitudinal axis of said structure being disposedin said plane while the major axis of said structure is disposed at anangle to said plane of 20 to '70 degrees.

5. In a device according to claim 2, said beam projecting meanscomprising an electrode structure having in cross section a major axisand a minor axis, the longitudinal axis of said structure being disposedin said plane while the major axis of said structure is disposed at anangle to said plane of 20 to 70 degrees.

6. In a device according to claim 5, the major axis of said structurebeing disposed at an angle of about 4.0 degrees to said plane.

7. In a multi-stage electron discharge device which utilises secondaryelectron emission for obtaining amplification, a thermionic cathode, acontrol electrode for controlling thermionic emission from said cathode,a first dynode comprising a structure conforming to a surface ofsubstantially elliptical cross section, said structure having secondaryelectron-emissive material provided on two areas on the inner siderespectively adjacent and on opposite sides of the ends or the majoraxis of said structure, a second dynode comprising two structureslocated respectively adjacent said areas and intersected by the planecontaining the major axis and the longitudinal axis of said first dynodestructure, said thermionic cathode and said second dynode structuresbeing enclosed by said first dynode structure and said cathode beinglocated between said second dynode structures, an electrode :forcollecting secondary electrons from said second dynode structures, andmeans for projecting electrons emitted from said cathode in oppositelydirected beams at an angle to pass, respectively, substantially whollyto one side of said second dynode structures and impinge on said areas,whereby to release secondary electrons which can impinge on said seconddynode structures.

8. In a multi-stage electron discharge device which utilises secondaryelectron emission for obtaining amplification, a thermionic cathode, acontrol electrode for controlling thermionic emission from said cathode,a first dynode comprising a structure one half of which is a mirrorimage of the other half and conforms to part of a surface ofsubstantially elliptical cross section whose major axis is inclined tothe major axis of the other half, said structure being provided withelectron emissive material on the inner side of each half adjacent theend of the corresponding major axis, a second dynode comprising twostructures disposed respectively within the halves of said first dynodestructure whereby each of said second dynode structures is intersectedby the plane containing the major axis and the longitudinal axis of thecorresponding half of the first dynode structure, said cathode beinglocated at the intersection of said planes. an electrode for collectingsecondary electrons from said second dynode structures, and means forforming electrons emitted from said cathode into oppositely directedbeams projected at an angle to pass, respectively, wholly to one side ofsaid dynode structures and impinge on said areas whereby to releasesecondary electrons which can impinge on said second dynode structures.

9. in a multi-stage electron discharge device which utilises seccndaryelectron emmission for obtaining amplification, a thermionic cathode, acontrol electrode for controlling thermionic emission from said cathode,a first dynode and a seconddynode, said first dynode being locatedbeyond said second dynode when viewed from said cathode and comprising astructure curved in cross section to be concave towards said seconddynode, said second dynode comprising an elongated member of smallerarea than said first dynode, a collecting electrode pervious toelectrons surrounding said second electrode, and means for projectingelectrons released from said cathode in a beam at an angle withreference to said second dynode to pass substantially wholly to one sideof said second dynode and impinge on said first dynode whereby torelease secondary electrons which converge on said second dynode.

CABO'I' SEATON BULL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,272,232 Wagner Feb. 10, 19422,293,417 Thompson Aug. 18, 1942

